No abstract

1. The phosphate requirement, i.e. the concentration of inorganic orthophosphate that just ceases to be limiting for growth, of Escherichia coli N.C.T.C. 5928 was determined for growth in ammonium-salts media containing glucose or acetate as the carbon and energy source, and compared with that of six other strains of E. coli. 2. The phosphate requirement for E. coli N.C.T.C. 5928 growing on acetate was about ten times that for growth on glucose, but this difference was not observed with any of the other strains. 3. After about 40 generations' growth on acetate with phosphate limitation in a chemostat, the phosphate requirement of the cells gradually decreased until it was equivalent to that of the glucose-grown organism; a single passage through glucose batch culture sufficed to restore the original high phosphate requirement, indicating a permeability phenomenon. 4. The lipid content of E. coli N.C.T.C. 5928 grown on glucose or acetate was measured isotopically by fractionation of cells grown on inorganic [(32)P]orthophosphate and gravimetrically after extraction from the cells by three different methods; change of carbon source from glucose to acetate did not affect the lipid content, which remained constant at 8-9% of the bacterial dry weight.

The effect of vacuum packaging on the microbial spoilage of 'ready-to-use' carrot slices and on the effect on shelf-life of the product is reported. The microbial development on vacuum packaged carrots was slower than that of non-vacuum packaged material. The predominant organisms present were Leuconostoc spp. in the vacuum packs as opposed to Erwinia spp. in the aerobic packs. Vacuum packaging of the sliced carrots significantly extended the shelf-life of the product when stored at 4°C from 5 to 8 days.

The production of ochratoxin A by Aspergillus ochraceus and of ochratoxin A and citrinin by Penicillium viridicatum growing on previously sterilised barley for 200 days at 5,lO and 20°C and a water activity of 0.85 is reported. A . ochraceus did not grow at 5"C, multiplied slowly at 10°C but did not produce toxin. At 20°C the organism multiplied more quickly and produced ochratoxin after 19 days, which slowly disappeared over the next 150 days. P. viridicatum grew slowly at 5°C but did not produce any toxin. It multiplied at 10°C and produced ochratoxin A which was only detectable during the period from 100 to 150 days. At 20°C both ochratoxin A and citrinin were produced. Ochratoxin A was detected after 10 days and was still present after 240 days, whereas citrinin was produced in large quantities between 118 and 129 days and then rapidly disappeared.

ABSTRACT

The production of patulin by P. expansum Link ex Gray growing in apple juice was determined over a range of pH. Patulin was found to be produced in large quantities over a narrow range of pH from 3‐2 to 3–8. The biomass produced increased with increasing pH. The changes in pH due to growth of the organism were found to be small.

The production of deoxynivalenol, acetyl deoxynivalenol and zearalenone by Fusarium culmorum and F. graminearum on autoclave‐sterilized grain (maize, rice, wheat and barley) was investigated. Fusarium culmorum produced significantly greater levels of toxins than F. graminearum. The four substrates examined differed in their ability to support toxin production. Toxin production on maize and rice was significantly greater than toxin production on barley or wheat.

Perennial ryegrass was inoculated with a mycotoxigenic strain of Fusarium roseurn or F. tricinctum and ensiled in laboratory silos to study the ability of the fungi to grow and produce toxin. Neither strain persisted in the silage or produced toxin. The addition of preformed toxin to the grass produced no detectable detrimental effect on the overall fermentation process.